1. Field of the Invention:
The present invention relates to a foam slush molding apparatus which performs molding and foaming simultaneously.
2. Description of the Prior Art:
Slush molding involves the basic steps of filling a preheated mold with a plastisol, which is highly viscous liquid composed of fine particles of plastics and plasticizer, causing the plastisol to stick to the inside of the mold, inverting the mold to pour out the excess plastisol, exposing the mold to heat for gelation of the sol sticking to the inside of the mold, and cooling the mold. This type of molding is conventionally called sol slush molding.
There is another type of slush molding, which is called powder slush molding. This molding process employs powdered resin.
The "foam slush molding" of the present invention can employ a sol or powdered resin containing a blowing agent and performs gelation and foaming simultaneously. This molding processes may be used for making automotive instrument panels which have a thin skin of, for example, plasticized polyvinyl chloride (PVC).
The heating and foaming of a resin containing a blowing agent are usually accomplished by the use of hot air or infrared radiation. For example, foamed PVC sheet is produced by passing an unrolled stock sheet continuously through a hot-air oven at about 200.degree. C. This foaming method is adequate for sheet-like objects which are uniformly heated. However, it is inadequate for objects of complex shape which are not uniformly heated. In the latter case, excessive foaming takes place on those parts sufficiently exposed to heat (such as periphery 1 and vertical surface 2 shown in FIG. 11) and insufficient foaming takes place on other parts which are not sufficiently exposed to heat. As a result, the foamed skin is unsatisfactory. The disadvantage of heating by infrared radiation is that undercuts and other parts are not exposed to radiation.
The present invention was completed in view of the above-mentioned circumstances. Accordingly, it is an object of the present invention to provide a molding apparatus capable of uniformly foaming the plastic or resin constituting a skin of complex shape.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.